Motor control with emergency stop



Nov. 25, `l947.` y Q.'M. BUNDY l 2,431,459

MOTOR CONTROLS WITH .EMERGENCY STOP File'd Sept. 14, 1944 5 Sheets-Sheetl Frm/@wer Nov.,25, 1947. o. M. BUNDY MOTOR CONTROLS WITH EMERGENCY STOPFiled Sept. 14, 1944 3 Sheets-Sheet 2 .i EMM. m5 n wm@ OW w uw MM Wm v..4 B

Nov. 25, 1947. o M. BUNDY n 2,431,459

MOTOR CONTROLS WITH EMERGENCY STOP Filed sept. 14, 1944 s sheets-sheet sffy 6 JNVENTOR. l Oswa/a/ML/na/q WMMQM Patented Nov. 25, 1947 MOTORCONTROL WITH EMERGENCY sror Oswald M. Bundy, Cleveland, Ohio, assignorto The Clark Controller Ohio, a corporation of Ohio ApplicationSeptember 14, 1944, Serial No. 554,086

12 Claims. 1

This invention relates to electrical systems applicable to the controlof an electric motor to start and stop it, and to control its speed inaccordance with the character of the load driven by the motor, andrelates particularly to such motor control systems which provide forstopping the motor and its driven load in a very short interval of time.

As will appear hereinafter, the control is applicable to motors as usedin various arts, processes and industrial applications, in whichelectric motor power is used; but in Order to make a concrete disclosureof the invention, I have chosen to illustrate and describe it herein asapplicable to a motor which drives a stand of calender rolls for rollingsheet material, for example rubber, to preselected thickness. Suchcalender roll machines themselves are well known and may comprise anumber of rolls one above the other two-high, three-high, etc., throughwhich the material is fed. The attendants at such machines work in closeproximity to the rolls, and through carelessness or inadvertence theirhands or clothing may sometimes be caught and drawn into and between therolls; and for their protection against injury it becomes important tobe able to stop rotation of the rolls instantaneously or as nearly so aspossible. Also, the material as fed to the rolls is often of irregularthickness; and in the case of rubber, for example, a lump of thematerial too large to be rolled may start to feed into the rolls; and itsometimes therefore becomes necessary to stop the rolls instantaneouslyto prevent jamming them by the material and spoiling the work, or toprevent damage to the machine.

Again, it is desirable to drive such rolls at high speed in the regularproduction of Work, but to be able to drive them at a low or creepingspeed, or with a start and stop inching movement, when a job of work isbeing started; and thereafter to be able to speed up the rolls to theoptimum high speed for the particular material being worked.

When the rolls are driven by an electric motor as here contemplated, thecontrol for the motor must therefore provide means for starting andstopping it with inching movements; operating it at variable low speed;variably adjusting the speed to a high production speed; and to be ableto instantaneously stop the motor when running at high speed upon theoccurrence of any emergency such as those mentioned above which mightotherwise cause injury to the workmen at Company, Cleveland,

2 the machine or to the machine itself, or to the work.

It is well knownthat in any application of motor power Where a widerange of speed variation is wanted, the direct current type of motor isoften the most practicable; and it is also well known that a directcurrent motor can be braked by dynamic braking, by connecting it in alocal circuit in which it acts as a generator and by dissipating theenergy of the generated current load in a resistor; but the usualdynamic braking control falls short oi the requirements of anapplication such as that outlined above.

Also, in prior practice, it has been found that where a motor is to beoperated throughout a wide range of adjustable speed, the full ratedtorque and power of the motor cannot be developed at all speeds if it besupplied from mains always at the same voltage; and this has led to theprovision of supply mains at two or in some cases three differentvoltages, a change over from one voltage to another being made as thespeed of the motor is changed from one part of its speed range toanother; and this obviously has led to complications and expense in thecontrol system.

In some cases in prior practice, it has been proposed to supply thecurrent to the motor from a generator provided for that specificpurpose, and to vary the voltage supplied to the motor by varying theoutput voltage of the generator; and in this manner some of thedecienoies of a single voltage motor control have been obviated; butsuch systems have not been adaptable to, and have not provided theinstantaneous stopping of, the motor in emergencies as above mentioned.

According to the present invention, and speaking generally, a directcurrent motor for driving the load is supplied with power from a directcurrent generator driven by a constant speed power source motor, forexample an alternating current induction motor; and means is providedfor varying the speed of the load driving motor over a very wide rangeand in an improved manner, by a control system actuated by a singleconstant voltage; and emergency stop means is provided which when putinto operation weakens the field of the generator to weaken its voltagein an improved manner by a plurality of concurrent actions, andelectrically brake the motor in an improved manner by a plurality ofconcurrent actions; whereby the voltage of the generator` is ultimatelydestroyed and the motor is brought to rest in the minimum period oftime. Y

It is therefore the object of the invention to provide an improvedmethod and means by which a load driving motor can be adjusted 1n speedover a Wide range for normal operation; and by which, upon theoccurrence of an emergency can be stopped in the minimum of time.

The invention is fully disclosed in the following description, taken inconnection with the accompanying drawing inwhich:

Fig. 1 `is a diagrammatic viewsillustrating an embodiment of theinvention.

Fig. 2, Fig. 3, and Fig. 4 are in each case views to enlarged scale ofcertain contactors of Fig. 1 and illustrating modifications, thereof;

Fig. 5, Fig. 6, and Fig. '7 are views similar-,respectively to parts ofFig. ;l -but'showi-ng Vmodications.

In the embodiment of the invention illustrated i normal condition, thatis when the windings `are -de-energized; andthe entire-system -isillustrated withthe -parts in normal unergized condition.

ATo simplify the drawing so that 'the various electrical circuits may berepresented in the socalled across-the-line type of diagram, adopt- -edby engineers generally, each contactor is shown-complete as Vhaving allof 'its contacts associatedwith it unitarily, but with the -circuitconnections to the contactsshown fragmentarily and broken off; and :eachAof these contacts is reproduced fragmentarily elsewhere in the diagramlwith the 4complete circuit connections thereto.

The contactors and their contacts are as follows:

Contactar LV having open contacts LVI LV'I inclusive and closedcontactsLVB.

YContactor `D having open contacts DI and closed contacts D2.

yContactor yDBR, having open contacts DBRI, and closed c ontactsDBRZ.

Contactor ACR having open contacts AGRI and ACRZ and closed contactsACRS.

`Contacter A having open contacts AAI and closed contacts A2.

Contactor YDB having open contacts 'DBI Yand closed contacts DB2.

.Contacter `SU having open contacts SUI and ASH2 and closed contacts SUSto SUB inclusive.

Contactor RN `having 'open contacts RNI to RNA inclusive.

Contactor GF having open contacts GFI to GF4 inclusive.

Contactor -GFA having open contacts fG'FAI and GFA2.

.Contactor GEB having open 4contacts GFBI Contactor -GFC having -opencontacts `GFCI and vGFCZ.

Contactor GFD having open contacts GFDI and closed contacts GFD2.

`Contactor VR having open contacts VRI.

At I is the -source of power motor, which in the embodiment-illustratedis a squirrel cage induction motor supplied by polyphasemains I, 2, and 3; and it is connected by a shaft 4, Yto the directcurrent generator G, to drive it, substantially at the constant speed ofthe source motor I. An exciter -E is also driven by the source motor Iand supplies direct current to mains 5 and E, at substantially constantyvoltage for operating the control system.

At M is the load driving motor, the shaft 'I 4 of which is connected tothe load t0 be driven, not shown.

The generator G has a shunt neld winding 8, and the load motor M has ashunt field winding I0.

Various resistors, circuit connections, operators contactors, and otherelements of the system not identied above will bedescribed in connectionwith a description cf 'the operation of the system as a Whole which nowfollows:

When the source motor I is started and brought n,to speed andvdrives'the rotor of the generator G, it also drives the exciter E andenergizes the controlmain-s `5 andfS and maintains themenergized-atsubstantially a constant potential.

The shunt field I0 of the load driving motoi 1i/Lis :at this ,timeenergized directly across the mainsg and 6 through the closed contactsLV8` but these contacts will presently be opened for normal operation,and vthe eld winding I0 will then .he .energized .through a .rheostat I2Aand a nxed .valueresistor ".I3,:the.rheostat I2 when op- -eratedladjusting the energization of .the eld windingforithepurposes ofvarying the-speedof :the .motor 'M .in the upper ranges yof its speed,,andthe .resistor I3 predetermining the maximum Ydegree to vwhich the'iield :Il'I .may 4be adjustably energized, for speed control.

`Atthisftime, alsothe contactor A .is energized acrossthesmains 5 and Vlthrough wires iIII, I5, ,IB, 'I1-and V-I and throughthe closed contactsACES. The contacts AI :are accordingly closed vand the contacts A2 open.Otherwise the systern remains unenergized.

The eld'winding 8 of lthe `generator 'G 'is at this timenotfenergized.Itis shown lin the draw- -ing -as connected Vacross the'terminals of theygen- -erator G `by -wi-re I9, closed contacts SU4, :wires 2B, r2I, ,22,`23, closed contacts SUS, vand wire 24; but although the :generator G isYbeing driven, this shunt -field winding -does not 4build up' and`energize the generatorasmightbe expected ffrom inspection -of `thedrawing -because the polarity .of 4the potential which might thus -besupplied .from 4the generator G to the iield 8 through the circuit justdescribed and which might result `iironrany .residual magnetism of theeld wind- .ing v8, ,is in .the .direction to .reduce the residual,magnetism or .de-.magnetize the generator field to zero excitation,.from .which it cannot .build up in the other direction.

To .put ,thesystern into operation, a Stop-Reset switch 25 which may be-of the push button type, .and .which has normally closedcontacts 26 and,normally open `contacts 27, is depressed .by the operator. This makesa. circuit from the main `5 through thenow closedcontacts 21, closedcontacts SU, wire 28, winding of the contactor LV, through closedemergency switch 29, to the line 6; and contactor LV being thereby.energzed, operates, Yclosing its contacts LVI to LVI inclusive andopening its contacts LVB. The resultof opening contacts LVB wasdescribed above.

Closing of contacts LV3 makes a'holding circuit for the contactor LV,from the main 5 Vthrough closed emergency switch 30, through the nowclosed closed contacts LV3y .through the winding of contactor LV andemergency switch 2,9, to main 6; so that when the stop-reset switch ,2 5is released, opening the contacts 2I (and closing contacts 26) the.contactor LV will remain operated.

The Said operation of the stop-reset switch 25 also causes current tonow through the contacts 21 and SUS as before, and by wire 3I throughthe winding of contactor D, through now closed contacts LV4 and LV5 tomain 6, operating contactor D and closing its contacts DI and openingits contacts D2.

Current now flows from lmain 5 through wire I4, through now closedcontacts DI, through winding of contactor DBR, and by wire 32 to main 6,operating contactor DBR, closing its contacts DBRI, and opening itscontacts DBRZ.

A resistor 62, in series with the winding of contactor D, is normallybridged by the closed contacts DBR2, so that the contactor D is operatedby full energizing current, but upon opening of contacts DBRZ, thisresistor reduces the current in the winding of contactor D to so low avalue that it is barely enough to hold the contactor D operated, wherebyit will be restored instantly and instantly close its contacts D2 (for apurpose to be described) when its current is broken.

Current now flows from the wires I4 and I5 through now closed contactsDBRI, through winding of contactor ACR, and by Wires 33 and 32 to main6, operating contactor ACR and closing its contacts ACRI and ACR2 andopening its contacts ACR3. This contactor operates instantly whenenergized, but in some cases it may be desirable to adjustably delay itsrestoring when de-energized to delay closure of its contacts ACR3 for apurpose to be referred to. This adjustably delayed restoring has notbeen shown in Fig. 1; but may be provided by any well known means, andis shown diagrammatically in Fig. 2 where the contactor ACR isreproduced to larger scale. A piston 63 in a cylinder 64 and attached tothe plunger G5 lifts a ball check valve B5 for unre' tarded upwardmovement of the plunger, and upon downward movement of the plunger, theair in the cylinder under the piston escapes through a port 61adjustably restricted by a screw Valve B8.

The opening of contacts ACR3 opens the line I8 through which the windingof contactor A was energized, but the contactor A remains energizedbecause the current therethrough can flow through closed contacts LV5and by wire 34 upwardly and through closed contacts LV5 to main 6, thisbeing a holding circuit for the contactor, A.

Closing of contacts ACR2 (contacts A2 being open) causes current to flowfrom main 5, by wire 35 through now closed contacts ACRZ, by wire 36,through the winding of contactor DB, and i by wire 31 to main I,operating contactor DB and closing its contacts DBI and opening itscontacts DB2.

Contacts DBI are in the line of the winding of contactor SU, but thiswinding is not at this time energized upon closure of contacts DBI,because the circuit is open both at the contacts VRI and RNI- Thestop-reset switch may now be released and the winding of contactor LVremains energized through the holding contacts LVS; winding of contactorD remains energized through closed contacts LV3, wires 2S and 3l,resistor 62, and closed contacts LV4 and LV5; winding of contactor DBRremains energized through contacts DI; winding of contactor ACR remainsenergized through contacts DBRI; winding of contactor A remainsenergized through contacts LV6 and LV5; winding of contactor DB remainsenergized through contacts ACR2; and the system is now ready to beoperated to energize the field of the generator G, and cause it tosupply current to the load motor M and drive it.

To do this, the start switch 38 which may be .6 of the push button type,is closed by the operator, and current then flows from the main 5,through the upper and now closed contacts 26 of the stopreset switch 25,by wire 39, through the contacts 40 of the start switch through closedcontacts GFDZ and SUG, and through Winding of contactor RN, throughwires 4I and 34 and thence through contacts LV5, to main 6, operatingcontactor RN and closing its contacts RNI to RNII inclusive.

Closing of contacts RNI energizes the winding of the contactor SU, thecurrent flowing from wire 5, through closed contacts RNI, through closedcontacts DBI, and winding of contactor SU, to wire 31, to main 6, andthe contactoriSU operates, closing its contacts SUI and SU2, and openingits contacts SU3 to SUS inclusive.

The operation of the contactor SU, by closing contacts SUI, establishesa holding circuit for contactor RN, independently of the start switch38, current flowing from the wire 3B, by a wire 42, through now closedcontacts SUI and RNZ, and by wire 43 through the winding of contactor RNand so on, so that although contacts SUG are now open, the winding ofcontactor RN remains energized, and the start switch can now bereleased; and the contactor SU wil1 also remain operated, through thecontacts RNI as described.

Since opening of contacts SUE opens the operating circuit for contactorRN, and closing of contacts SUI closes a holding circuit for it, it maybe desirable to insure that contacts SUB open after contacts SUI close.This may be accomplished by any known means in contactor constructiongenerally, and is not shown in Fig. 1, but is shown diagrammatically inFig. 3, wherein when the plunger 'II is raised by energization of thewinding, and raises the stern 12, bridging bars 'I3 to 'I6 and a headI'I and bridge secured to the stem rise with it. The stem 'I2 passesthrough a perforation 'I8 in a bridging bar I9 which normally bridgescontact elements -80 of the double break contacts SUS. The bars 13 and'I4 normally bridge contact elements 8I-8I and 82-82 of the double breakcontacts SUI and SU2, and are supported on yieldable springs 83-83 and84-84. After contacts SUI (comprising the bar I3 and contact elements8I-8I) have closed, the stem 'I2 continues to rise and the head 'IIengages the bar 19 and raises it from the contact elements Bil-80.

When contactor RN operated and closed contacts RN3, current also iiowedthrough contacts GFD2, SUB, wire 43, contacts RNS, through winding ofcontactor GF, and through closed contacts LV'I, wire 34, contacts LV5 toline 6, operating contactor GF and closing its contacts GFI to GF4; andwhen contacts SUI closed and SUG opened, a holding circuit for contactorGF was made, independent of the start switch 38, by wires 39 and 42,contacts SUI and RNZ and RNS, and through winding of contactor GF and soon.

Referring now to the upper part of the diagram, it will be observed thatcontacts SU3 and SU4 are now open, disconnecting the generator' field 8from the generator G; and that contacts LVI are closed; and thatcontacts GFI and GF have just closed; so that current will now besupplied to the generator field 8, from the mains and ii. At 44 to 5Iinclusive are generator eld resistors or sections of resistance,controlling the energization of the generator eld d. The contacts ACRIare closed as described, as are also conta-cts LV2 and GF3, so thatfield current now Vflows from the main 5, through the contacts GFI, LVI,resistor 44, contacts GF3 and LV2 .and by wire 52, to the point 53; andfield current also flows by wire 54 and wires 22 and 2I, through the eldwinding 8, and by wire Y52 te the peint 53, in parallel with theresistor 44; and from the peint 53 the eld current flows through theresisters 48 to 5I in series, and through the closed contacts GFZ te themain 8, establishing the minimum eld strength for the generator yG andindependently of its own potential.

The polarity of the potential producing this generator field is oppositeto that which the generator G itself would supply to the field winding 8if the contacts SUS and SU4 were closed, as was described above.

The driven generator G new develops its minimum potential due to saidminimum field energization, and supplies current to the load motor M,the current flowing over the heavy line circuit by wire 55, throughclosed contacts AI, wire 58, (contacts D2 being open), through the loadrneter M, by wires El, 58, and '58, back to the generator G, and thefield winding I of the motel M being energized as described, (LVS beingopen) the motor M starts and rotates slowly at its minimum load drivingspeed, in its low speed range.

The system new operates to cut out successively the resistors 48 to 5Iinclusive, by means ef the contacts GFAI to GFDI inclusive, tostrengthen the 'held 8 of the generator G and cause it to applyincreasing potential to the 'motor M te increase its power and speed,and this sequence will be apparent in the lower part of the diagram.

`When the contacter GF operated, and closed its contacts GF-, currentthen ilowed from the main 5, through already closed contacts RN4, SU2,and through contacts GF4, through wire 69, energizing the winding ofcontacter GFA, and by wire 6I te wire S4 and contacts LVE, to main 8;and contacter GFA operated closing contacts lGFAI and GFA2.

The closing of contacts GFAI cuts out resister 48 (er an adjustable partof it as will be described) at the top of the diagram.

'The closing of contacts GFAZ energizes the 'winding of contacter GFB,and it operates, the current flowing from wires 68 and 62 through thecontacts GFAZ and through said Winding to wire -BI and 34, etc,'Operation of ycontacter GFB closes its contacts GFBI and GFBZ. ContactsGFBI cut out eld resistor f4.8, and contacts GFB2 energize the windingof contacter `GFC, which operates, closing its contacts GFCI which cutout resistor 5), and closing its contacts GFCZ which energizes thewinding of contacter GFD. Contacter GFD upon operating closes itscontacts GFDI which cuts out resistor 5I, and opens its contacts GFD2.

'The power delivery of motor M and the speed thereof is thus increased,and if all of field resistor 48 is cut out, the motor comes up to what:is sometimes called its base speed. The rheostat LI 2 may new beoperated to cut resistance into the circuit of the motor eld winding IIl, and the speed of the motor M may thereby be increased into itshigher speed range, either to attain its maximum speed or to adjust itsspeed to the optimum high speed for the particular load being driven,the particular material being worked upon by the machine being driven,etc.

If however it be desired to operate the motor at base speed, therheostat I2 will be left in its illustrated condition for maximumoperating strength of the motor eld Il).

And again, if it be desired to operate the motor at less than basespeed, the ield 8 of the gencrater G (and its corresponding voltage), iscorrespondingly weakened by adjustment of the field resistor 48. Asshown, the movable adjusting Contact may be moved te peints along theresistor 48 (for example to position 85A) so that when the contacts GFAIclose, a part of this resister will be left in the field energizingcircuit.

Thus the operating speed of the meter M may be adjusted to any desiredvalue, at or above, or below the base speed.

The krate at which eld resistors 48 to 5I inclusive .are successivelycut out, may be predetermined by delaying the operation of thecontactors GFA to GFD inclusive, after their windings have beenenergized. This has not been shown in Fig. l, but may be effected by anywell known means and is illustrated diagrammatically in Fig. Zl for thecontacter GFA as an example, wherein a known dash-pot arrangement isshown comprising: a piston 86 connected te the stern 81 and plunger 88and retarded in its upward movement in a cylinder 89 by a restricted airinlet port 198, adjustable by a screw valve 8|, a ball check valve 92 inthe piston permitting the piston to return without retardation.

Referring again to the start switch 38, when it is rst closed itoperates contacter RN and then contacter GF, and closure of contacts GF4initiates the sequential cutting out of the eld resistors to acceleratethe motor M. But contactors RN and GF cannot be thus operated unless thelast of the sequential field resistor centactors, GFD, is de-energizedand its contacts GFDZ are closed. This insures that all of the eldresistors will be in the field circuit at the time of accelerating themotor M.

Also, after operation of contacters RN, GF, and SU by the start switch38 as described, the contacter RN maintains control of contacter SU atcontacts RNI and maintains control of contacter GF at contacts RN3; butafter contacter SU opens contacts SUG, contactors RN, GF, and SU are outof control of the start switch 38, and are controlled by the holdingcircuit including stopreset contacts 26, wires 39 and '42, contacts SUI,RNZ, wir@ 43, winding of contacter RN, wire 4I etc.

The contacter SU is controlled by the contactor VR at the contacts VRIsupplemental to its control by the contacter RN at the contacts RNI. Thewinding of the contacter VR is energized across the generator G by itspotential. As will be clear later, when the contacts RNI are opened, thecontacts VRI will maintain the contacter SU operated so long as thegenerator voltage is above a preselected value, predetermined by theoperating constants of the contacter VR, unless the contacts DBI havealready opened.

Thus the generator eld 8 rst becomes energized at GFI and GF2 with aweak energizatien as described, upon operation of GF by start switch 38,and then at any time, before or after its energization is increased, themaintenance of its energization is placed on the contacts 26 of thestop-reset switch 25. Operating the stop-reset switch to open itscontacts 28, will thus deenergize the contacter GF and disconnect thegenerator eld 8 from the supply mains 5 6 at contacts GFI and GFZ andreinsert any field resistors 48 to 5I which may have been cut out, andalso will de-energize the contacter RN which de-energizes the contacterSU (at RNI) and the latter causes the contacts SUS and SU4 to connectthe field 8 te the reverse polarity of the generator G te reduce itsresidual iield magnetism.

Now since the motor M can be driven by current from the generator onlywhen the generator field 8 is energized, it follows from the above thatthe motor M can be started by operating the start switch 38 to close itscontacts 4D, and can be stopped again by depressing the stop-resetswitch to open its contacts 26, whereby a creeping or inching movement;of motor M may be had for Well known purposes, such as those referred tohereinbefore.

As indicated in the foregoing, one ,of the primary improvements effectedby this invention is that upon the occurrence of an emergency the motorM may be stopped abruptly and in a shorter interval of time than isbelieved to be possible with any prior control system, and this featureof the invention will now be described, the advantages of the inventionin this respect being more fully developed and apparent in an instancein which the motor M is running at high speed arrived at as describedabove.

The generator G will at this time be developing full voltage, and thecontactor VR will be operated thereby, holding its contacts VRI closed.

At 29 and 3i) have been illustrated two emergency switches and these arecontemplated to be located at different points adjacent to the machineattendants, and within their convenient reach, and there may be anynumber of such switches corresponding to the switch 29, and any numbercorresponding to the switch 30, and this has been indicated byillustrating another of such switchesZSA in dotted line. These emergencyswitches may have any suitable or known construction and preferably are.of the push button type operable by a touch of the hand or arm or foot.Upon operation and opening of the contacts of any one of such emergencyswitches,

contactor LV will be die-energized, since the holding circuit thereforis, as shown, through these emergency switches in series; and upondeenergization of contactor LV, the following circuit changes occurwhich will be first described, and then these will be given adescription of the effects of such changes.

Contacts LVI open and disconnect the field 8 of the generator G from themains and 6; contacts LV2 open and remove the bridge which they effectedacross the field resistors 46 and 41; contacts LVB close and shortcircuit, all of the resistance in the circuit of the motor field I0,thus giving it a forced or excessive energization.

Contacts LV4 and LV5 open and de-energize contactor D which opensinstantly due to its resistor 62; and the opening of contacts LV5deenergizes the contactors RN, and (as a consequence thereof) GF, GFA,GFB, GFC, GFD; contactor SU is not de-energized, being maintained bycontacts VRI and DBI; and the opening of contacts LVS and LV5 (contactsACR3 being open) de-energizes the contactor A.

The said de-energizing of contactor D instantly closes its contacts D2and this closes a dynamic braking circuit around the load motor Mcomprising the wire 56, contacts D2, resistor RBI, resistor RB2(contacts DB2 being open) and wire 51; and the opening of contacts DIdeenergizes contactor DBR.

Closure of contacts D2 also closes a local load circuit around thegenerator G comprising wire 55, resistor RS (AI being open) wire 56,contacts D2, resistors RBI and RB2, and wires 58 and 59.

The said de-energizing of contactor GF opens contacts GFS and removesthe bridge from the field resistor 45.

The said de-energizing of contactor DBR opens contacts DBRI and therebyde-energizes contactor ACR.

The said de-energizing of contactor ACR effects opening of contacts ACRIand removes the bridge from the field resistor 41, and effects delayedclosing of contacts ACR3 which when closed again energize contactor A.

Contactor A upon being re-energized closes contacts AI short circuitingthe said resistance RS, and by opening its contacts A2 de-energizescontactor DB.

The. said de-energizing of contactor DB closes contacts DB2, shortcircuiting the dynamic braking resistance section RBZ; and openscontacts DBI.

Contacts RNI have already opened upon deenergization of contactor RN asabove referred to, so that now opening of contacts DBI deenergizescontactor SU (unless it has already been de-energized by opening ofcontacts VRI).

The contactor SU upon being de-energized closes contacts SU3 and SU4associated with the generator field circuit.

These changes and the sequence in which they occur, and their effects,stated briefly, are:

The field 8 of the generator G is cut off from the supply mains 5 and 6at LVI, and eld resistor 46 is cut in at LV2; and the field IIJ of themotor M isexcessively energized, or forced at LV8.

A dynamic braking circuit is closed around the motor M at D2 throughresistors RBI and RB2; and a local load circuit is closed around thegenerator G at D2, including resistor RS and the resistors RBI and RB2;and the eld resistor 45 is cut in at GFS.

The field resistor 41 is cut in at ACRI.

The resistor RS is cut out at AI.

The resistor RB2 is cut out at DB2.

The contactors SU3 and SU4 close.

The effects of these changes to quickly stop the motor M are as follows:

To stop the motor M, it is contemplated that the eld of the generatorwill be weakened and ultimately destroyed so that the generator willcease developing voltage and4 supplying current to the motor; and thatthe motor M itself will be dynamically braked; and that the motor M willsupply current to the generator G which in turn will further brake themotor M. But to do this in the quickest possible time, a number ofinteractions and quantities and sequences have been found necessarywhich are not obviously apparent from the foregoing.

The generator eld 8 must be weakened at the maximum rate possibleWithout developing a destructive field discharge voltage, and this isdone by several concurrent actions. The field is energized by a closedloop circuit connected across the lines r5 and 6, the field 8 beingenergized in parallel with its resistor 44 in this loop, so that whenthe loop is cut off from the supply lines at LVI, this loop becomes adischarge circuit without other change or provision, and the fieldstarts to decay, or discharge, safely. The discharge circuit at thistime contains resistors 44 and 46. A low resistance local load circuitis closed around the generator G which includes the resistors, RS, RBI,and RBZ. The generator supplies local load current to this local circuitand the resistor RS is given such ohmic value that, at the start, thislocal current is the maximum current which the generator armature cansafely carry and cornmutate, and in consequence, this current in thegenerator armature produces a field demagnetizing armature-reaction ofthe maximum possible degree which reduces the effective field flux andreduces the voltage.

The generator voltage producing field iiux is thus concurrently weakenedboth by armature demagnetization reaction, and by the dying out ordischarging of the field through the eld resistors 156 and 44.

The voltage of the generator thus dies out at a much more rapid ratethan if the field energization alone were weakened, or if it merely diedout at the maximum safe discharge rate alone.

Furthermore, the field flux is caused to progressively die out fasterand the generator voltage to be reduced faster, by the successivecutting in of field resistors 45 and 41.

While this very rapid weakening of the generator iield and voltage isgoing on, the motor M is acting as a generator and is being dynamicallybraked and rapidly slowed down by a braking circuit including the sameresistors RBI and RB2, and this braking action is magnified byartificially increasing or forcing the motor eld to an excessive degreeof energization, the value of the braking current thus controlled by theresistors being made at the start, the maximum value of current whichthe motor armature can carry and commutate.

At the start the dynamic braking of the motor M and the weakening of thegenerator field go on independently of each other (except for the commonutilization of resistors RBI and RB2); but after a brief period of timethe voltage of the generator becomes less than the counter voltagek ofthe motor M acting as a generator, and this time period is reduced tothe minimum by effecting rapid reduction of the generator voltage asdescribed.

The motor M then begins to supply current to the generator G whichbrakes the motor in addition to its own dynamic braking current. Thegenerator G being connectedV to the source motor I, which preferably isa squirrel cage induction motor, tends to act as a motor itself anddrive the induction motor above synchronism as a generator; butbecauseof the steep torque curve of the induction motor, its speed will beincreased very little, so that the generator G as a motor will increaseVery little in speed, and its counter voltage will present substantiallyno increased opposition to the voltage from the motor M, so that themotor` M will now be braked both by its own dynamic braking current andby the current supplied to the generator.

rihe eld and voltage of the generator G continue to die out, but thecurrent supplied. to the generator G by the motor M to brake the motoris maintained at a high braking value notwithstanding that the motorvoltage itself dies out also due to its slowing down, because thedecrease of one voltage is compensated by the decrease of the other.

As the motor M slows down and its voltage as a generator decreases, andas the voltage of the generator G also decreases, each is able to carryand commutate more current; the contacts AI threfore can now close andby snorting the resistor RS boost the braking current from the motor M;to-the generator G safely. The continued further reduction of thevoltage of generator G to a value farther and farther below that of themotor M still farther boosts or increases this braking current. Theshorting of the braking resistor RB2, still further brakes the motor Mby boosting the current in the dynamic braking circuit.

The field of the generator is finally completely destroyed by closing ofthe contacts SU3 and SU4, and the generator armature then is driven bythe source motor I Without developing any voltage, and is in a shortcircuit across the motor M; and this in addition to the low resistanceloca] dynamic circuit across the motor M accompanied by very low voltageof the motor due to its reduced speed provides a total braking currentof 200% to 400% of the current which it can carry at normal voltage. Themotor torque therefore rises to a Very great value and brings the motorto rest.

It will be noted from the above that the closure of contacts AII to givea boost to the braking current from the motor M to the generator G, andthe closure of the contacts DB2 to boost the local dynamic brakingcurrent of the motor M, are timed by adjustably delaying the restoringof contactor ACR. When it restores and c1osescontacts ACRS', contactor Aoperates and. closes contacts AI, snorting resistor RS. Contactor A thenalso opens contacts A2 which de-energize contactor DB and the lattercloses contacts DB2 and shorts the dynamic braking resistor RB2.

It is desirable to time the, contactor ACR so that the contacts AI willshort the resistor RS (to be followed by shortingV of resistor DB2) atjust about the instant when the voltageA of motor M balances or equalsthe falling voltage of the generator G, so thatthe resistor RS will notrestrict current from the motor to the generator; and the contactor ACRis timed and set to bring this about. However it isalso desirable tohave contacts SUS and SU 4 close to finally destroy the generator fieldas soon as thisl can be done with-` out causing a dangerous peak in themain current; but (in the absence of other provisions) the contactor SUwill. be de-energized and close the contacts SUS and SU4' upon openingof contacts DBI and the contacts SU3 and SUB will thus be timed by thecontacter ACR, which times the contactor DB.

Depending upon the speed of the motor when the emergency stopisinitiated, the voltage of the generator may have fallen to the value atwhich the-contacts SU3' and SU4 can safely be closed', before th-e settiming of contactor ACR effects openingof contacts DBI. In such eventtheA contactor VR Will restore and open its contacts VRI andV causecontacts SU3` and SUI!v to close independently of the opening ofcontacts DBI by the said timing.

It will be observed that when the contacts D2 close, they simultaneouslyestablish a load circuit across the generator G and a` dynamic brakingcircuit across the motor M. In the present embodiment this as shown canbea common bridging circuit, comprising common, resistors RBI and HB2.The electrical loading of thegenerator Gk for field demagnetizingpurposes, and the electricalv loading of the motor M for brakingpurposes are therefore both produced by a single set of circuitelements; so that by thetime that the resistor RB2 is cut out of thiscircuit, and. boosts the dynamic braking current of the motor M, themotor-is already being braked by current to the generator G and thisbraking current is added to the boosted dynamic braking current.

The simplication and. economy afforded by this provision, and` theproducing of the said effects simultaneously to keep them coordinated13'y and without lapses cf time between them are among the advantages ofthis invention.

According to the foregoing when emergency stop is initiated the eldmagnetism and Voltage of the generator G is rapidly weakened by cuttingoil the energizing potential from the loop circuit of the feid 8; andallowing it to discharge at a controlled safe rate in that loop circuit;and by electrically loading the generator G by a local circuit toproduce armature-reaction-demagnetization; and by connecting the held 8to the generator G with reverse demagnetizing polarity.

As a further means, to effect still more rapid reduction of thegenerator eld magnetism and voltage, a generator with a series fieldwinding may be utilized. In such cases I prefer to put the series eldwinding in the circuit as indicated at 93 in Fig. 5. Otherwise thesystem of Fig. 5 may be the same as that of Fig. l.

In the operation of this modification, the normally closed contacts Alkeep the series eld winding 53 shorted along with resistor RS, duringnormal operation of the generator G and load driving motor M, so that itdoes not function like the usual generator series field winding. Duringemergency stopping, and as described for Fig. l, contacts D2 close alocal circuit for the generator for armature-reaction demagnetizingpurposes and the contacts Al open to include the resistor RS in thelocal circuit to predetermine the maximum demagnetizing local current,and at the same time they include the eld winding 93 in this circuit.The terminals of the field winding 93 are connected in this circuit asto polarity so that the magnetomotive force produced in it by this localcurrent is opposite to that of the eld winding 8, whereby it exerts ademagnetizing action on the generator eld.

The contacts A! close at, or about, the time that current from the motorM starts to flow in the other direction to the generator G as described,s that the winding 93 is shorted and does not build up nux in thegenerator iield in the other direction which would tend to retard thefalling of the generator voltage.

In some instances it is of course desirable to stop the motor M withoutemergency-stop, when the motor is running at regular production speed;and this is done by depressing the stop-reset switch to open itscontacts 26. This cuts off the holding current from contactor RN, and itrestores; and its contacts RN2 open and prevent it from operating againwhen the stop-reset switch is released; and its contacts RN# open andrestore all of the field resistor controlling contactors GFA to GFD,reinserting all of the eld resistors 48 to 5l; and its contacts RNS openand restore contactor GF whose contacts GFI and GF2 open and cut off theloop circuit of the generator field 8 from the lines 5 5, and whosecontacts GFS insert resistor 45 into the generator eld discharge loopcircuit.

The field and voltage of the generator thus decay by discharge, in aloop circuit whose resistance controls the rate of discharge to a safevalue.

Contactor SU is, for a time, held operated by contacts VR! and DBI(contacts RNI having opened), but when the generator voltage has fallensuiiciently, contactor VR will restore and open its contacts VRI,thereby restoring contactor SU, and its contacts SU3 and SU4 thereuponclose and completely destroy the generator eld. The motor M is braked tostop it, by supplying current (as a generator) to the generator G whenthe generator eld and voltage have become sufliciently weakened. Thecontacts Al are closed and the armature of the generator is in a lowresistance path across the motor armature, by way'of circuit 56, Al, 55,59, 58, and 51. Stopping the motor M in this manner when running atproduction speed will be seen to be similar to stopping it duringinching.

The emergency switches 29 and 35 have each been shown in Fig. 1 asbreaking the circuit to the winding of contactor LV at a point betweenthe winding and only one of the supply mains, 5 or 5. In some cases, asa safety precaution, it may be desirable to arrange the construction ofthese emergency switches and their connections so that any one of themwill break the supply current at both sides of the winding. Suchpossible arrangements are believed to be known to those skilled in theart and it is thought to be unnecessary to illustrate or describe them.

In Fig. 1, for inching movements of the motor M, the motor is started bythe start switch 38 and is stopped by the stop-reset switch 25. In somecases it may be desirable to eiiect starting and stopping inchingmovements on a single push button switch, and the modication of Fig. 6shows how this may be done.

The start switch, here 38A, besides its contacts 155, has contacts 45Anormally bridged by a switch 94. This modication is otherwise the sameas Fig. 1, and when the start switch contacts 4!! are closed, thecontactors RN, SU, and GF operate as before, and the series ofaccelerating contactors GFA to GFD (of which only GFA is shown) operateto start and speed up the motor M, and it can be stopped only at thestop-reset switch 25,

For inching with this arrangement, the switch 94 is rst opened and leftopen. Then upon operating the start switch 38A, the contacts 45A takethe place of the switch 9e, and so long as both of its contacts 45 and40A are held closed the contactors RN, SU, GF operate and again startand speed up the motor; but the holding circuit for the contactors RN,SU, and GF is by'way of the wire 39 as hereinbefore described, and thecontacts 40A are in the line of this wire, so that when the start switchis released and opens its contacts 40A, the holding circuit is openedand the contactors RN, SU, and GF, etc., all restore and the motor Mstops.

It was explained above that it is desirable, upon emergency stopping ofthe motor M, to have the contacts Al close to short out the resistor RS(and also the series ield 93 of the generator G when utilized as in Fig.5) at just about the instant when the voltage from the motor M balancesthe rapidly falling voltage of the generator G; and one means wasdescribed for doing this by adjustment oi the delayed return ofcontactor ACR to close its contacts ACR3.

Another or modified way to do this; and which will be independent of theproduction speed of the motor M when emergency stopping is initiated, isshown in Fig. '7 parts not shown in this iigure being the same as inFig. l.

The contactor DBR has an additional pair of normally open contacts DBR3;and these are in a line from the wire l5, to a wire 95, to the winding aof an additional contactor CR and thence to the wire 32 and line 6. Thecontactor CR has also a winding b connected across the resistor RS.

The contacts ACR3 are omitted from the contactor ACR.

Upon starting up the motor M, upon closure of T contacts Dl, contactorDBR operates. Its. contacts BERE effect operation of contactor CR bywinding aA and its contacts, CRI open, leaving the contactor A energizedthrough contacts LVS and LVS, and holding its contacts AI closed.

During emergency stop, whenV contactor LV restores, and contacts LVt,yopen,v contactor A restores and opens contacts Al inserting resistor RS,and the generator G- is loaded b-y current through wire 55, resistor RS,wire 5S,y etc., as described. This causes a drop of potential across.the resistor RS which energizes winding bof contactor CR as a holdingwinding.

When contacts DI open de-energizing contactor DBR, and contacts DBR! andDBR3 open and de-energize contactor ACR and winding a of contactor CR,contacter ACR restores opening its contacts ACR!4 and ACRl with theresults described ior Fig. l, but contactor CR is held operated bywinding c and still holds contacts CRI- open, keeping contactor Ade-energized.

When the-voltage of motor M balances. the fall-- ing voltage orgenerator G,l current stops flowing in` the resistor RS and the holdingwinding b accordingly becomesde-energized and contactor CR restores,closing its contacts CRiand this energizes contacter A which closescontacts Al and shorts the resistor RS for the purposes referred to.

The contacts CRI thus take the place of contacts ACRE of Fig. l, butyclose in response to balanced voltages of the motor and generator,

insteady of being given a set timed closure as were the contacts ACRE ofFig. 1.

The invention is not limited to the exact details of construction,illustrated, and described.

Changes and modifications may be made, and theV invention comprehendsall Such changes and modifications which come within the scope of theappended claims.

I claim:

l. In a motor control system, a direct-current load-driving-mctorsupplied by current froma direct-current generator having a currentenergized field and connected in series with the motor, and means toeffect quick stopping of the motor comprising means for quickly reducingthe generator voltage by weakening its eld energization, andelectrically loading the generator independently of its motor load tocause further weakening of the generator eld by armature demagnetizingreaction, and concurrently dynamically braking the motor,

2. In a motor control system, a direct-current load-driving-motorsupplied by current from a direct-current generator having a currentenergized field and connected in series with the motor, andV means toeffect quick stopping of the motor comprising meansV for quicklyreducing the generator voltage by Jeakening its eld energization, andelectrically loading the generator independently of its motor load tocause further weakening Ofj the generator iield by armaturedemagnetizing reactionT and concurrently dynamically braking the motor;and comprising means to subsequently cause further braking of the motorby the current load thereof supplied to the generator effective afterthe voltage of the generator has fallen below that of the motor.

3. In a motor control system, a direct-current load-driving-motorsupplied by current from a direct-current generator having a currentenergized field and connected in series with the motor, and means toeffect quick stopping of the. motor comprising means for quicklyreducing the generator voltage by weakening its field energization,

and electrically load-ing theA generator independently oi its, motorloa-,dr tocause further weakening off the generator field by armaturedemagnetizing reactiom and concurrently dynamically braking the motorand comprising means to. subsequently cause further braking oi the motorby the current load. thereof supplied to the generator effective afterthe voltage of the generator has fallen-below that of the motor;concurrently with continued dynamic braking of the motor.

4. In a motor control system,V a direct-current load-driving-motorhaving an energized shunt eld, and connected in a series circuit with adirect-current generator having an energized shunt field, and means toveiTect quick stopping of the, motor comprising circuit means bridgingboth the generator and the motor to electrically load the generator andcause weakening of its field and voltage byarmature-reaction-demagnetization, and to. alsoelectrically loadthemotor as a generatorto dynamically brake it; and means to concurrentlyadditionally weaken the generator iield and voltage comprising meansdiscontinuing the energization of the generator eld, and establishing adischarge circuit for it, and controlling the rate oiits discharge.

5.V In a motor control system, a direct-current load-driving-motorhaving an energized shunt eld, andconnected in a series circuit with adirect current generator having an energizedv shunt field, and means toeffect quick stopping of the motor comprising circuit means bridgingboth the generator and the motor to electrically load the generator andcause weakening of its eld and voltage byarmature-reaction-demagnetization, and to also electrically load themotor as a generator to dynamically brake it; and means to-concurrentlyadditionally weaken the generator eld and voltageV comprising meansdiscontinuing the energization of the generator field, and establishinga discharge circuit for it, and controlling the rate of its discharge;and means controlling the electrical load of the generator, andcontrolling Y the braking electrical. load of the motor.

6. In a motor control system, a direct-current load-driving-motor havingan energized shunt field, and connected in a series circuit with adirect current generator having an energized shunt eld, and means to.eirect quick stopping of thcmotor comprising circuit means bridging boththe generator and the. motor. to electrically load the generator andcause weakening of its eld and voltageY byarmature-reaction-demagnetization, and to also electrically load themotor as a generator to dynamically brake it; and means to concurrentlyadditionally weaken the generator field and` voltage comprising meansdiscontinuing the energization of the generator field, and establishinga discharge circuit for it, and controlling the rate. of its discharge;and means controlling the resistance of the said circuit means andthereby controlling the electrical load of the generator and the brakingelectrical load of the motor.

'1. In a motor control system, a. direct-current load-driving-motorhaving an energized shunt eld, andV connected in a series circuit with adirect-current generator having an energized shunt eld, and means toeiiect quick stopping` of the motor comprising means forcing theenergization of the motor eld; circuit means bridging both the generatorand the motor to electrically load the generator and cause weakening ofits eid and voltage. by armature-reaction-demagnetization, and to alsoelectrically load the motor as a generator to dynamically brake it; andmeans to concurrently additionally weaken the generator eld and voltagecomprising means discontinuing the energization of the generator field,and establishing a discharge circuit for it, and controlling the rate ofits discharge; means causing the motor to supply current t the generatorover said series circuit to further brake the motor effective uponreduction of the generator voltage by said held-weakening; and meanseffecting energizing of the generator field by reversed polarity gf thegenerator to nally destroy the generator eld.

8. In a motor control system, a source of direct current at constantpotential; a generator driven at substantially constant speed and havinga shunt field winding energized from the source; a power-supplying motorsupplied with current from the generator and having a shunt eld windingenergized from the source; means to control energization of thegenerator field to start and stop the motor with inching movements;means to vary the generator eld energization to vary the motor operatingspeed within a first range of speeds; means to vary the motor eldenergization to vary its operating speed Within a second range ofspeeds; and emergency stop means for the motor comprising: means toforce energization of the motor field, contacter means to disconnect thegenerator eld winding from the source, a discharge circuit for thegenerator iield winding, contacter means to vary the resistance of thedischarge circuit, a local circuit for bridging the generator and themotor and contactor means to close it, and the local circuit havingresistance of preselected value to cause current from the generator inthe local circuit to further weaken the generator field and voltage byarmaturereaction-demagnetization, the local circuit also effectingdynamic braking of the motor, and means to vary the resistance of thelocal circuit.

9. In a motor control system, a source of direct current at constantpotential; a generator driven at substantially constant speed and havinga shunt field winding energized from the source; a power-supplying motorsupplied with current from the generator and having a shunt eld windingenergized from the source; and emergency stop means for the motorcomprising: means to force energization of the motor field, contactermeans to disconnect the generator eld Winding from the source; adischarge circuit for the generator field Winding, contacter means toVary the resistance of the discharge circuit, a local circuit forbridging the generator and the motor and contactor means to close it,and the local circuit having resistance of pre-selected Value to causecurrent from the generator in the local circuit to further weaken thegenerator field and Voltage by armaturereaction-demagnetization, thelocal circuit also effecting dynamic braking of the motor, and means tovary the resistance of the local circuit.

10. In a motor control system, a source of direct current at constantpotential; a generator driven at substantially constant speed and havinga shunt field winding energized from the source; a power-supplying motorsupplied with current from the generator and having a shunt eld windingenergized from the source; and emergency stop means for the motorcomprising: contacter means to disconnect the generator eld winding fromthe source, a discharge circuit for the generator eld Winding, contactormeans to Vary the resistance of the discharge circuit, circuitconnections and contacter means for closing a loading circuit across thegenerator to electrically load it, the loading circuit comprisingresistance of preselected Value to cause the electrical load to furtherweaken the generator field by armature-reaction-demagnetization, meansto vary the resistance of the loading circuit, and a variable-resistancedynamic-braking circuit for the motor, at least a part of the resistanceof the loading circuit being common to the dynamic braking circuit.

11. In a motor control system, a direct-current load-driving-motorconnected in a circuit in series with a direct-current generator, andmeans to effect quick stopping of the motor comprising means weakeningthe generator eld and voltage by weakening the field energization, andelectrically loading the generator independently of its seriesconnection with the motor to cause concurrent further weakening of thegenerator eld and voltage by demagnetizing armature reaction; meansdynamically braking the motor, independently of its series connectionwith the generator; and, means concurrently additionally braking themotor by braking current from the motor in the series circuit throughthe generator, eiective upon weakening of the generator iield.

l2. In a motor control circuit and apparatus system, a pair of directcurrent supply mains; a generator driven by a source of power and havinga shunt field winding always connected in a loop in parallel with firstfield resistance and the loop being connected in series with secondiield resistance; a motor in series with the generator and supplied withcurrent from the generator and having a shunt field winding energizedfrom the source; means to start and stop the motor comprising means toconnect one supply main to the loop and the other supply main to thesecond field resistance and to control the total iield resistance, andto disconnect the said mains; emergency means to quickly stop the motorcomprising: means to effect disconnecting of the generator iield loopfrom the supply mains and to allow it to discharge in the loop to weakenits eld and voltage; and comprising means to eiect closing of localcircuit means across the generator and the motor, having predeterminedresistance to cause the motor to be dynamically braked at the maximumsafe rate and to also cause the generator to be electrically loaded tothe maximum safe degree, independently of its series connection with themotor to weaken its eld and voltage byarmature-reaction-demagnetization; and comprising means to control theresistance of the local circuit means to cause the motor to supplyunrestricted current to the generator to further brake the motor afterweakening of the generator voltage to balance that of the motor, andindependently of continued dynamic braking of the motor; and comprisingmeans to destroy the generator field and voltage by reverse energizationof its field winding.

OSWALD M. BUNDY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 696,017 Dutton Mar. 25, 19022,249,857 Schaelchlin July 22, 1941

